Device for the thermal erasure of mechanically readable optical markings

ABSTRACT

An apparatus adapted for thermally erasing or changing machine readable optical markings previously entered on a carrier of thermoplastic material which has two major sides, and wherein the optical markings cause a predetermined modification of any light rays impinging on the optical markings by either diffraction or refraction, include a erasing device adapted to be located on one major side of the carrier, for erasing or changing the markings, a reading device, operative during operation of the erasure device, and including at least two light sensors adapted to be located on the other major side of the carrier, so as to check the erasure or change of the markings effected by the erasing device. The light sensors provide output signals of respective opposite polarities following erasure or change of any one of the markings. A moving device generates a relative movement between the carrier and the erasing and reading devices, respectively, and a comparator is postcoupled to the light sensors, and includes a detector for indicating whether the output of the comparator exceeds or is below respective predetermined limits. A control device controls the operation of the erasing device of the moving device and is arranged to inhibit the operation of the erasure device when the output of the comparator exceeds or falls below the limits, respectively, so that the limits establish a uniform criterion for effecting erasure of the markings.

BACKGROUND OF THE INVENTION

A device is known from the Swiss patent (CH-PS 574 144), in which acard-like or tape-like payment-means contains a multitude of units ofvalues in form of mechanically readable optical markings which, to givean example, can be holograms or diffraction screens. For cashlesspayments for goods or services rendered, the payment-means aredevaluated step-by-step in accordance with the amount to be paid, namelyin that the markings are thermically erased by means of a transparentheating element. A reading-light-beam is directed through thetransparent heating element to a marking, the marking is then checked bymeans of light sensing elements for genuineness, is then erased and bymeans of signals obtained from the light sensing elements, a check isperformed whether the marking has been actually erased.

Furthermore, a method for the production of a document is known fromSwiss patent CH-PS 594 935, in the case of which a multitude of opticalmarkings, which for example can be holograms or diffraction screens, arerecorded on a carrier and in which, for the purpose of writing in acode, selected markings are then subsequently erased. The erasing of themarkings takes place by means of heating elements, which consist of aresistance layer which, in turn, has been applied onto a substrate.

Hannan, U.S. Pat. No. 4,108,367, although having some similarities withthe present invention, does not attain the objects of the presentinvention. Both the light source and the light sensors postcoupled tothe comparator are disposed on one side of the carrier. The outputsignals of the light sensors do not have respective opposite polaritieswhen a marking is erased, nor is the reading means operable during theerasure process, as the light rays are interrupted by the erasing head.The duration of the erasure process is determined by the delay of theerasure means in starting and terminating erasures, and is independentof the fact whether or not an adequate erasure has been obtained.

The German laid open patent specification DE 26 59 639 teaches readingmeans and an erasure head disposed on the same side of a document, andtherefore teaches away from the present invention.

Schaffer, U.S. Pat. No. 2,975,282 teaches how to copy information from acredit card by means of a lamp onto one side of a sales ticket, and isnot relevant to the present invention.

Hickey et al, U.S. Pat. No. 3,921,969 is not relevant other thandocumenting the fact that a moving or transportation device fordocuments is known.

It should be added that British Pat. No. 1 502 460 is equivalent toSwiss Pat. No. 574,144, and that U.S. Pat. No. 4,143,810 is equivalentto Swiss Pat. No. 594,935.

OBJECT OF THE INVENTION

The invention recited in claim 1 has as its objective of improving thequality of the erasing process by simple measures and to assure that,for the purpose of attaining a rapid action and/or an optimum use of theenergy available for the erasing process, the marking is sufficientlyerased, but not to an unnecessarily high degree.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, a few exemplified embodiments will be explained inmore detail with reference to the drawings.

FIG. 1 shows a card-like carrier.

FIG. 2 shows the carrier according to FIG. 1 in a magnifiedcross-section,

FIG. 3 shows a coding device for a carrier according to FIG. 1,

FIG. 4 shows portions of a coding device,

FIG. 5 shows a block-circuit-diagram of the coding device,

FIG. 6 shows a heating element in an enlarged side view,

FIG. 7 shows the heating element of FIG. 7 in a cross-sectional view and

FIG. 8 shows an erasing head with a projection lamp.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, 1 denotes a card-like carrier made of thermo-plasticmaterial, which carrier can be an identification card, an admissioncard, a credit card, a monetary instrument, a check, a transportationticket, a monetary substitute card, or the like. This carrier 1 includesa timing track 2, which in turn, advantageously includes three differenttypes of optical time-markings 3, 4, and 5, which are arranged in acyclic sequence. Furthermore, the carrier 1 includes a data track 6 withoptical markings 7, which data track 6 is disposed in parallel with thetiming track 2 which optical markings initially follow one anotherwithout the formation of any gap. The boundary line between the adjacentmarkings 7, which is in effect not visible, results from the geometricarrangement of the time-markings 3, 4 and 5. These time-markings and themarking 7 are entered or impressed onto the carrier 1, and differ fromthe marking-free surface of the carrier 1 by a mechanically detectablecharacteristic modification of any impinging light brought about throughdiffraction or refraction. Accordingly, the markings can for example, bediffraction screens, holograms, cinema-forms, Fresnel-lenses, etc.

By means of the coding device illustrated in FIG. 3, coded informationis fed to the data track 6, this being accomplished in that selectedmarkings 7' are thermally erased, in other words are changed to such adegree while using heat, so that they no longer bring about the samecharacteristic modification of the impinging light, as the unchangedmarkings 7.

In the illustrated example, the carrier 1 shown in FIG. 2 consists of athermo-plastic layer 8 with impressed marking 7 in form of a phasediffraction screen, consisting of a thin reflecting layer 9 and acovering layer 10. The covering layer 10 is impervious to light and thecarrier [-layer] 8 is permeable, for example, to infrared reading lightbeams, but, is impervious to visible light.

The coding device illustrated in FIG. 3 includes a screw 11 foradvancing the carrier 1, which screw 11 is mounted in a rotatable mannerin a housing 12, and is connected with a driving motor which is notillustrated. When the screw 11 is being driven, it carries along a cardholder 13 in a linear manner and thereby moves the carrier 1, which isreceived in a receiving-slit 14, between a reading head 15 and anerasing head 16. Within the effective range of the reading head 15 andthe erasing head 16, the card holder 13 is formed with openings 17. Thereading head 15 includes light sources 18, 19 and light sensing devices20 to 24, wherein the light source 18, as well as the light sensingdevices 20, 21 are assigned to the data track 6, and the light source19, as well as the light sensing devices 22 to 24 are assigned to thetiming track 2. Each of the light sensing devices 22 to 24 responds toone of the time markings 3 to 5. A non-erased marking 7 excitespredominantly the light sensing device 20, and an erased marking 7'predominantly excites the light sensing device 21.

FIG. 4 shows an advantageous embodiment of the erasing head 16. Thelatter contains a heating element 25 in form of a metallic yoke, whichis bent in form of a P, so that one extremity of the metallic yoke,spaced at a distance from its middle portion by means of an insulatingpiece 26, is mounted to the middle portion by means of rivets 27consisting of insulating material. The erasing portion 28 of the heatingelement 25 is placed on an area which approximately corresponds to thatof the markings 7. The heating element 25 is mounted in a rotatablemanner on a stationary plate 29, and is prestressed by means of a spring30, which--in the operating position assumed by the heating element 25during the erasing process of a marking 7'--ensures that the erasingportion 28 abuts the top of the covering layer 10 of the carrier 1,while exerting a predetermined pressure thereon. In the rest position ofthe heating element 25, the force of a spring 31 opposes the force ofthe spring 30, and lifts the heating element 25 from the carrier 1,through the action of a solenoid armature 32 and a pull rod 33. When asolenoid coil 34 is excited, the pull rod 33 releases the heatingelement 25, which--through the force the of spring 30--is then pivotedinto the working position. The heating element 25 is connected to thesecondary winding of a transformer 35, which furnishes a current which,in turn, flows directly through the heating element 25.

In FIG. 4, also the arrangement of the light sources 18, 19 and of thelight sensing devices 20 to 24 is indicated, which are located on theside of the carrier facing away from the erasing head 16, in other wordsthey are located on the side of the layer 8.

As can be seen from FIG. 5, two of respective elements 36 through 38 oflight sensing devices 22 to 24 are in each case connected to the twoinputs of a comparator. If, to give an example, a time marking 3 passesby the reading head 15, and if a time marking 4 follows the time marking3, then the signal of the light sensing device 22 decreases continuouslyand that of the light sensing device 23 increases continuously duringthe transition from the time marking 3 to the time marking 4, however,an impulse-shaped output signal is obtained from the comparator 36.

The light sensing devices 20 and 21 are connected with a comparator 39.If a marking 7', which is located between the reading head 15 and theerasing head 16, is erased, the signal of the light sensing device 20decreases and that of the light sensing device 21 increases. Animpulse-shaped output signal from the comparator 39 is obtained, as soonas the thermal effect has brought about an erasure of the marking 7'which is considered adequate.

The comparators 36 to 39 are connected to a control device 40, whichevaluates the signals of these comparators and controls the erasing head16, as well as the driving motor which, in FIG. 5, is designated withthe reference numeral 41.

The control device 40 contains an input device which is not illustrated.This input device receives a code, which, through erasing of themarkings 7' is to be recorded on the carrier 1. A voltage is applied tothe transformer 35, so that the heating element 25 is heated to acertain temperature. The control device 40 starts up the driving motor41, and the carrier 1 which had been introduced into the card holder 13passes between the reading head 15 and the erasing head 16. By meansfrom the signals of the comparators 36 to 38, a counter in the controldevice 40 counts the time markings 3 to 5 which have passed by thereading head 15. A comparison-unit of the control device 40, comparesthe counting state of this counter with the code received by the inputdevice. In case of an agreement, that is to say if a marking 7', whichis to be erased, is present within the effective field of the readinghead 15 and the erasing head 16, the driving motor 41 is stopped and thesolenoid coil 34 is excited. The heating element 25 moves into a workingposition, the carrier 1 is heated in the area below the erasing portion28 and the marking 7' is erased, that is to say, in the describedexample the embossment structure of the impressed phase diffractionscreen reappear. During the erasing process, which takes a certain timewhich, in turn, depends on the temperature of the heating element 25, onthe ambient temperature and on the consistency of the carrier 1, thereading unit is in operation, which consists of the light source 18, thelight sensing devices 20, 21 and of the comparator 39. As soon as theoutput voltage of the comparator has fallen below a predetermined level,so that the marking 7' coming in contact with the heating element hasbeen erased sufficiently, the control device 40 interrupts the currentsupply to the solenoid coil 34, as a result of which the heating element25 is lifted-off from the carrier 1, and restarts the driving motor 41.

The advantages of the invention are now easily recognizable. The erasingprocess is not interrupted at a predetermined time period, but isimmediately interrupted at the point when a sufficient erasing of themarking 7' has been achieved. In this manner, a sufficient erasure isalso guaranteed under different working conditions, an excessive erasureof the marking 7' which is to be erased is avoided, as well as anyundesired erasure of adjoining markings 7 and, depending on theapplication, a high operating speed and/or an optimum use of theavailable energy is achieved. The arrangement of erasing head 16 on theone side of the carrier 1 and the arrangement of the reading head 15 onthe other side of the carrier 1, makes possible the simultaneous erasureand monitoring of the erasing by simple means.

The afore described scanning and counting of the time markings 3 to 5during the search for positions to be erased on the data track 6, makespossible a very accurate positioning of the erasing head 16 at theposition to be erased, which positioning is independent of thelongitudinal tolerances of the carrier 1. If the carrier support 1 isdevoid of any time-markings then, to give an example, the leading edgeof the carrier 1 or the leading edge of the data track 6 can serve asposition reference for locating the positions to be erased. In this casea stepping motor serves advantageously for driving the screw 11, whichstepping motor moves the card holder 13 forward by a constant amountwith each step, so that a certain number of steps brings about a forwardmovement of the card holder 13 by a distance which corresponds to thespacing of the markings 7. This allows one, without any intervention inthe mechanic of the selecting device assigned to the control device 40,to preselect the number of steps of the stepping motor in accordancewith the spacings of the markings 7 and to change therewith the spacingat any time in such a manner, so that carriers using differentrespective spacings can be encoded with the same coding device.

In order to be also able to adjust the height of the erasing head 16 andof the reading head 15 with respect to the longitudinal edge of thecarrier 1, to the conditions existing each time, the depth of thereceiving slit 14 (FIG. 4) can be advantageously changed by means of anexchangeable insert 42.

The afore described erasing head 16, the heating element 25 of which ispressed onto the carrier 1 during the erasing process and is lifted-offtherefrom for the interruption of the erasing process, makes possible ahigher operating speed, but, requires a relatively large amount ofenergy.

If, for the purpose of erasing the markings 7', only a small amount ofenergy is available, which is the case for example, when dealing withtelephone sets which draw the energy for the erasing of the markings 7'from the subscriber's loop, then an erasing head 43 as shown in FIGS. 6and 7 is used to advantage. This erasing head 43 contains a heatingelement 44 with a low heat capacity, the current supply of which, forthe purpose of interrupting the erasing process, can be cut-off. In theillustrated example, the heating element 44 consists of a resistancelayer which has been produced through screen printing processes or hasbeen deposited through evaporation, and which is arranged on a substrate45, and is provided with electrical contacts 46. In order to keep theenergy consumption at a low level, the substrate 45 consists of a poorlyheat-conducting material, for example of glass or of a ceramicsubstance. Furthermore, the substrate 45 is shaped in form of atruncated pyramid, in order for its thermal resistance to decrease withan increasing distance from the heating element 44, and in order for theenergy flowing into the substrate to be quickly dissipated aftertermination of the erasing process. A recess 47 serves to obtain auniform wall thickness of the substrate 45, so as to prevent materialstresses and strains.

Depending on the consistency of the covering layer 10 (FIG. 2) of thecarrier 1, better results of the erasing process are achieved witheither an erasing head abutting the carrier 1, or with a contactlesserasing head which acts as heat radiating element. FIG. 8 shows acontactless erasing head 48 with a projection lamp 49, which serves asheat radiating element and is arranged at a distance from the carrier 1.A diaphragm 50 shields the carrier 1 from the heat radiation, with theexception of the areas to be erased.

Prior to the coding on the carrier 1, the projection lamp 49 is heatedto the operating temperature, so that the heat radiation impinges on thecard holder 13 and remains ineffective. Subsequently, the driving motor41 is started and the carrier 1 is advanced at such a high speed, sothat the radiation of heat no longer brings about a noticeable change inthe data track 6. As soon as a position to be erased is reached, thedriving motor 41 is stopped and the heat radiation brings about theerasing of a marking 7'. After an adequate erasure, the erasing processis cut-off through a renewed activation of the driving motor 41.

In the case of a carrier having a relatively low softening value, it canbe of advantage to operate the projection lamp 49 at a reduced voltageduring the advancement of the carrier 1, and to increase the voltage tothe nominal value only after reaching an erasing position.

With an optical image producing system, which is not illustrated in FIG.8, the degree of effectiveness of the erasing process can be improved.It is also possible to use an electronic flash bulb as heat radiatingelement, in place of the projection lamp 49. We wish it to be understoodthat we do not desire to be limited to the exact details of constructionshown and described, for obvious modifications will occur to a personskilled in the art.

Having thus described the invention, what we claim as new and desire to be secured by Letters Patent, is as follows:
 1. An apparatus adapted for thermally erasing or changing machine readable optical markings previously entered on a carrier of thermoplastic material having two major sides, the optical markings causing a predetermined modification of any light rays impinging on said optical markings by either diffraction or refraction,comprising in combination: erasing means adapted to be located on one major side of said carrier, for erasing or changing said markings, reading means, operative during operation of said erasure means, and including at least two light sensors adapted to be located on the other major side of said carrier, so as to check the erasure or change of said markings effected by said erasing means, the light sensors providing output signals of respective opposite polarities following erasure or change of any one of said markings, moving means operable for generating a relative movement between said carrier and said erasing and reading means, respectively, a comparator postcoupled to said light sensors, and including detection means for indicating whether the output of said comparator means exceeds or is below respective predetermined limits, and control means for controlling the operation of said erasing means and of said moving means, and arranged to inhibit the operation of said erasure means when the output of said comparator means exceeds or falls below said limits, respectively, whereby said limits establish a uniform criterion for effecting erasure of said markings.
 2. An apparatus as claimed in claim 1, wherein said erasing means includes heating means movable between a first position near said carrier during erasure or change of said markings, and a second position remote from said carrier during interruption of the erasure or change of said markings.
 3. An apparatus as claimed in claim 1, wherein said erasing means includes heating means of relatively low thermal capacity having a current supply which may be switched off during the erasure period or change period of said markings.
 4. An apparatus as claimed in claim 3, wherein said erasing means includes a substrate having substantially the shape of a truncated pyramid, said heating means being disposed near the smaller end surface of said truncated pyramid, and a resistance layer formed with electrical contacts disposed on said substrate.
 5. An apparatus as claimed in claim 1, wherein said erasing means includes heat radiation means spaced apart from said carrier, and wherein the erasure or change of said markings may be interrupted by moving said moving means rapidly away from said carrier.
 6. An apparatus as claimed in claim 5, wherein said heat radiation means includes a projector lamp.
 7. An apparatus as claimed in claim 5, wherein said heat radiation means includes an electronic flashlight.
 8. An apparatus as claimed in claim 1, wherein said moving means includes a rotatable gear, a drive motor coupled to said gear, and carrier-holding means connected to said gear and linearly drivable thereby.
 9. An apparatus according to claim 8, wherein said markings are spaced from one another by respective predetermined distances, said drive motor is a stepping motor advanceable in a plurality of discrete steps, and wherein said control means includes selection means for selecting said plurality of steps in dependence of said predetermined distances.
 10. An apparatus as claimed in claim 1, wherein said reading means includes at least one additional light sensor adapted to scan said optical markings, and wherein said control means includes a counter for counting the scanned optical markings, input means for receiving the code, and comparing means for comparing the count of the counter with the code received by said input means, and for initiating erasure or change of one of said markings when said code coincides with said count.
 11. An apparatus for thermally erasing or changing machine readable optical markings,comprising in combination: a carrier of thermoplastic material having two major sides, said optical markings having been previously entered on said carrier, and causing a predetermined modification of any light rays impinging on said optical markings by either diffraction or refraction, erasing means arranged to be located on one major side of said carrier, for erasing or changing said optical markings, reading means, operative during operation of said erasure means, and including at least two light sensors arranged to be located on the other major side of said carrier, so as to check the erasure or change of said markings effected by said erasing means, the light sensors providing output signals of respective opposite polarities following erasure or change of any one of said markings, moving means operable for generating a relative movement between said carrier, and said erasing and reading means, respectively, a comparator postcoupled to said light sensors, and including detection means for indicating whether the output of said comparator means exceeds or is below respective predetermined limits, and control means for controlling the operation of said erasing means and said moving means, and arranged to inhibit the operation of said erasure means when the output of said comparator means exceeds or falls below said limits, respectively. 